U.S. patent number 8,501,148 [Application Number 12/148,920] was granted by the patent office on 2013-08-06 for coating composition incorporating a low structure carbon black and devices formed therewith.
This patent grant is currently assigned to Cabot Corporation. The grantee listed for this patent is James A. Belmont, Jeremy K. Huffman, Andriy Korchev, Agathagelos Kyrlidis, Geoffrey D. Moeser. Invention is credited to James A. Belmont, Jeremy K. Huffman, Andriy Korchev, Agathagelos Kyrlidis, Geoffrey D. Moeser.
United States Patent |
8,501,148 |
Belmont , et al. |
August 6, 2013 |
Coating composition incorporating a low structure carbon black and
devices formed therewith
Abstract
A black matrix or coating includes carbon black including a
first carbon black having an I.sub.2 number from 30 mg/g to 200
mg/g and a DBP from 20 cc/100 g to 45 cc/100 g.
Inventors: |
Belmont; James A. (Acton,
MA), Moeser; Geoffrey D. (Reading, MA), Korchev;
Andriy (Billerica, MA), Kyrlidis; Agathagelos (Malden,
MA), Huffman; Jeremy K. (Amarillo, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
Belmont; James A.
Moeser; Geoffrey D.
Korchev; Andriy
Kyrlidis; Agathagelos
Huffman; Jeremy K. |
Acton
Reading
Billerica
Malden
Amarillo |
MA
MA
MA
MA
TX |
US
US
US
US
US |
|
|
Assignee: |
Cabot Corporation (Boston,
MA)
|
Family
ID: |
39535632 |
Appl.
No.: |
12/148,920 |
Filed: |
April 23, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080269379 A1 |
Oct 30, 2008 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60926003 |
Apr 24, 2007 |
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60963815 |
Aug 7, 2007 |
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Current U.S.
Class: |
423/449.1;
524/59; 524/495; 106/476; 106/311 |
Current CPC
Class: |
C09C
1/48 (20130101); C09C 1/56 (20130101); G03G
9/0926 (20130101); C09C 1/565 (20130101); C09C
1/50 (20130101); C01P 2006/12 (20130101); C01P
2006/80 (20130101); C01P 2006/22 (20130101); C01P
2006/19 (20130101); Y02P 20/129 (20151101); C01P
2004/51 (20130101); C01P 2002/52 (20130101) |
Current International
Class: |
C01D
3/00 (20060101); B41M 5/165 (20060101); C08L
95/00 (20060101); C09C 1/44 (20060101); B60C
1/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0420271 |
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Apr 1991 |
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EP |
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10-2005-0070947 |
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Jul 2005 |
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KR |
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10-0560713 |
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Mar 2006 |
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KR |
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WO03/057784 |
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Jul 2003 |
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WO |
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WO2004046244 |
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Jun 2004 |
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WO |
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Primary Examiner: Gregorio; Guinever
Parent Case Text
This application claims priority from U.S. Provisional Applications
Nos. 60/926,003, filed Apr. 24, 2007, and 60/963,815, filed Aug. 7,
2007, the contents of both of which are incorporated herein in
their entirety.
Claims
What is claimed is:
1. A black matrix comprising at least a first carbon black, the
first carbon black having an I.sub.2 number from 30 mg/g to 200
mg/g, a DBP from 20 cc/100 g to 39 cc/100 g, an M-ratio of from 1
to less than 1.24 and a concentration of Group IA and IIA elements,
in .mu.g/g, of at most y+(15*I.sub.2 number), wherein y is 250.
2. The black matrix of claim 1, wherein the first carbon black is
characterized by at least one of the following: the carbon black
has an M-ratio of from 1 to less than 1.22, the carbon black has a
pH from 6 to 10, the carbon black has a water spreading pressure of
at most 6 mJ/m.sup.2, the carbon black has a tint obeying the
equation tint=x+0.44*I.sub.2 number, where x is from 45 to 90, or
the carbon black has a tint of at least 80.
3. The black matrix of claim 1, wherein the black matrix has an
optical density of at least 3 at a 1 micron thickness.
4. The black matrix of claim 1, wherein the black matrix has a
surface resistivity of at least 10.sup.12 ohm/square at a carbon
black loading of at least 60%.
5. The black matrix of claim 1, wherein the black matrix comprises
a second carbon black.
6. The black matrix of claim 5, wherein the second carbon black
differs from the first carbon black in one or more of surface area,
structure, primary particle size, alkali and/or alkaline earth
concentration, pH, Spectronic 20 value, tint, or a surface
concentration of oxygen-containing groups.
7. The black matrix of claim 5, wherein the second carbon black is
an oxidized carbon black, a heat treated carbon black, or a
modified carbon black comprising an attached organic group.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the use of low structure carbon
blacks in curable coating compositions, curable coatings, and cured
coatings comprising carbon blacks, and black matrices that can be
formed therefrom.
2. Description of the Related Art
Black matrix is a generic name for materials used in color displays
to improve the contrast of an image by separating individual color
pixels. In liquid crystal displays (LCDs), the black matrix is a
thin film having high light-shielding capability and is formed
between the three color elements of a color filter. In LCD's using
thin film transistors (TFT), the black matrix also prevents the
formation of photo-induced currents due to reflected light in the
TFT.
The black matrix layer in liquid crystal displays has been
manufactured by vapor deposition of Cr/CrO. Although chromium based
films have excellent light-shielding capabilities, the metal vapor
deposition process is expensive. In addition, chromium use and
disposal is subject to increasingly restrictive environmental
regulations. Chromium films also have low resistivity, which
restricts the electrical design of LCDs to a subset of the possible
design configurations.
Black pigments such as carbon black have been used in polymer
compositions to make resistive black matrices. The structure and
surface area of these blacks are chosen to permit a particular
loading level of carbon black in a matrix and to reduce
conductivity and charge accumulation in the media. Increased
loading level increases the optical density (OD), a measure of the
opacity of a material, of the media but also increases the
viscosity of the coating compositions used to produce the media.
Thus, it is often difficult to achieve the desired balance of
overall properties. For example, while a black matrix containing a
carbon black pigment could provide the required light-shielding
capabilities (that is, a threshold optical density), the film might
have only a modest resistivity, limiting its ability to inhibit
photo-induced currents. Alternatively, if a highly resistive film
were produced, the OD might be too low to be commercially
viable.
Decreasing the structure of the component carbon black can decrease
viscosity, allowing thinner layers of the media to be deposited
without defects, or it can allow more carbon black to be
incorporated at a given viscosity, resulting in a higher optical
density. One method of controlling the structure of a furnace
carbon black is by adding alkali or alkaline metal elements to a
furnace while burning a carbonaceous feedstock. However, the
resulting metal component in the carbon black can contribute to
increased conductivity, and non-carbon materials in the media do
not contribute to optical density. Furthermore, as potassium and
other metal elements are added to the furnace, the resulting black
has more charged groups on the surface and is thus more
hydrophilic. Thus, a decrease in structure may come at the expense
of increased conductivity and decreased optical density resulting
from non-carbon elements in the carbon black. More hydrophilic or
acidic blacks (e.g., pH less than 6) may not be compatible with as
wide a range of polymers and other components that would be
otherwise desirable for use in coating or printing applications. In
addition, while optical density or tint may be increased by
increasing surface area, it becomes increasingly difficult to
decrease the DBP as the surface area is increased. Thus, it is
desirable to develop carbon blacks having low structure but also
having low amounts of alkali metals and high hydrophobicity and
that do not compromise electrical properties, optical density and
viscosity in compositions and devices incorporating the carbon
black.
SUMMARY OF THE INVENTION
In one aspect, the invention includes a black matrix including at
least a first carbon black. The first carbon black has an I.sub.2
number from 30 mg/g to 200 mg/g, a DBP from 20 cc/100 g to 45
cc/100 g, and a total concentration of Group IA and IIA elements,
in .mu.g/g, of at most y+(15*I.sub.2 number), wherein y is 250,
100, -50, -150, or -350. For example, the first carbon black may
have a DBP value of from 20 to 45 cc/100 g, from 20 to 30 cc/100 g,
from 25 to 43 cc/100 g, from 25 to 40 cc/100 g, from 30 to 39
cc/100 g, or a DBP in any range bounded by any of these endpoints.
Alternatively or in addition, the first carbon black may have an
iodine number (I.sub.2 number) of from 30 to 200 mg/g, for example,
from 30 to 45 mg/g, from 45 to 100 mg/g, from 60 to 80 mg/g, from
70 to 100 mg/g, from 100 to 150 mg/g, from 150 to 200 mg/g, 70 to
200 mg/g, or in any range bounded by any of these endpoints. The
first carbon black may be characterized by at least one of the
following: an M-ratio of from 1 to less than 1.25; a pH from 6 to
10; a water spreading pressure of at most 6 mJ/m.sup.2; or a tint
of at least 80.
In another aspect, the invention includes a black matrix including
at least a first carbon black, the first carbon black having an
I.sub.2 number from 30 mg/g to 200 mg/g, a DBP from 20 cc/100 g to
45 cc/100 g, and a water spreading pressure of at most 6
mJ/m.sup.2. For example, the first carbon black may have a DBP
value of from 20 to 45 cc/100 g, from 20 to 30 cc/100 g, from 25 to
43 cc/100 g, from 25 to 40 cc/100 g, from 30 to 39 cc/100 g, or a
DBP in any range bounded by any of these endpoints. Alternatively
or in addition, the first carbon black may have an iodine number
(I.sub.2 number) of from 30 to 200 mg/g, for example, from 30 to 45
mg/g, from 45 to 100 mg/g, from 60 to 80 mg/g, from 70 to 100 mg/g,
from 100 to 150 mg/g, from 150 to 200 mg/g, 70 to 200 mg/g, or in
any range bounded by any of these endpoints. The first carbon black
may be characterized by at least one of the following: an M-ratio
of from 1 to less than 1.25; a pH from 6 to 10; a total
concentration of Group IA and IIA elements, in .mu.g/g, of at most
y+(15*I.sub.2 number), wherein y is 250, 100, -50, -150, or -350;
or a tint of at least 80.
In another aspect, the invention includes black matrix including at
least a first carbon black, the first carbon black having an
I.sub.2 number from 30 mg/g to 200 mg/g, a DBP from 20 cc/100 g to
45 cc/100 g, and a pH from 6 to 10. For example, the first carbon
black may have a DBP value of from 20 to 45 cc/100 g, from 20 to 30
cc/100 g, from 25 to 43 cc/100 g, from 25 to 40 cc/100 g, from 30
to 39 cc/100 g, or a DBP in any range bounded by any of these
endpoints. Alternatively or in addition, the first carbon black may
have an iodine number (I.sub.2 number) of from 30 to 200 mg/g, for
example, from 30 to 45 mg/g, from 45 to 100 mg/g, from 60 to 80
mg/g, from 70 to 100 mg/g, from 100 to 150 mg/g, from 150 to 200
mg/g, 70 to 200 mg/g, or in any range bounded by any of these
endpoints. The first carbon black may be characterized by at least
one of the following: a total concentration of Group IA and IIA
elements, in .mu.g/g, of at most y+(15*I.sub.2 number), wherein y
is 250, 100, -50, -150, or -350; an M-ratio of from 1 to less than
1.25; a water spreading pressure of at most 6 mJ/m.sup.2; or a tint
of at least 80.
In another aspect, the invention includes a black matrix including
at least a first carbon black, the first carbon black having an
I.sub.2 number from 30 mg/g to 200 mg/g, a DBP from 20 cc/100 g to
45 cc/100 g, and an M-ratio of from 1 to less than 1.25. For
example, the first carbon black may have a DBP value of from 20 to
45 cc/100 g, from 20 to 30 cc/100 g, from 25 to 43 cc/100 g, from
25 to 40 cc/100 g, from 30 to 39 cc/100 g, or a DBP in any range
bounded by any of these endpoints. Alternatively or in addition,
the first carbon black may have an iodine number (I.sub.2 number)
of from 30 to 200 mg/g, for example, from 30 to 45 mg/g, from 45 to
100 mg/g, from 60 to 80 mg/g, from 70 to 100 mg/g, from 100 to 150
mg/g, from 150 to 200 mg/g, 70 to 200 mg/g, or in any range bounded
by any of these endpoints. The first carbon black may be
characterized by at least one of the following: a concentration of
Group IA and IIA elements, in .mu.g/g, of at most y+(15*I.sub.2
number), wherein y is 250, 100, -50, -150, or -350; a pH from 6 to
10; a water spreading pressure of at most 6 mJ/m.sup.2; or a tint
of at least 80.
In any of the above embodiments, the carbon black may have a tint
obeying the equation tint=x+0.44*I.sub.2 number, where x is from 45
to 90, for example, from 60 to 90 or 75 to 90. The black matrix may
include at least 50% by weight of carbon black, for example, at
least 55% by weight of carbon black, from 50% to 80% by weight of
carbon black, from 55% to 80% by weight of carbon black, or 60% to
80% by weight of carbon black. The black matrix may have an optical
density of at least 3, for example, at least 4, at a 1 micron
thickness. The black matrix may have a surface resistivity of at
least 10.sup.12 ohm/square at a carbon black loading of at least
60%.
In any of the above embodiments, the black matrix may include a
second carbon black. The second carbon black may differ from the
first carbon black in one or more of surface area, structure,
primary particle size, alkali and/or alkaline earth concentration,
pH, Spectronic 20 value, tint, or a surface concentration of
oxygen-containing groups. The second carbon black may be an
oxidized carbon black, a heat treated carbon black, or a modified
carbon black comprising an attached organic group.
In another aspect, the invention includes a curable coating
composition including a vehicle, a curable resin, and at least a
first carbon black. The first carbon black has an I.sub.2 number
from 30 mg/g to 200 mg/g, a DBP from 20 to 45 cc/100 g, and a
concentration of Group IA and IIA elements, in .mu.g/g, of at most
y+(15*I.sub.2 number), wherein y is 250, 100, -50, -150, or -350.
For example, the first carbon black may have a DBP value of from 20
to 45 cc/100 g, from 20 to 30 cc/100 g, from 25 to 43 cc/100 g,
from 25 to 40 cc/100 g, from 30 to 39 cc/100 g, or a DBP in any
range bounded by any of these endpoints. Alternatively or in
addition, the first carbon black may have an iodine number (I.sub.2
number) of from 30 to 200 mg/g, for example, from 30 to 45 mg/g,
from 45 to 100 mg/g, from 60 to 80 mg/g, from 70 to 100 mg/g, from
100 to 150 mg/g, from 150 to 200 mg/g, 70 to 200 mg/g, or in any
range bounded by any of these endpoints. The first carbon black may
be characterized by at least one of the following: an M-ratio of
from 1 to less than 1.25; a pH from 6 to 10; a water spreading
pressure of at most 6 mJ/m.sup.2; or a tint of at least 80. The
carbon black may have a tint obeying the equation
tint=x+0.44*I.sub.2 number, where x is from 45 to 90, for example,
from 60 to 90 or 75 to 90. When the curable coating composition has
a carbon black loading of at least 50% by weight, it may exhibit
Newtonian flow. The curable coating composition may have a carbon
black loading of at least 20 weight %, at least 30 weight %, at
least 40 weight %, at least 45 weight %, at least 50 weight %, at
least 55 weight %, or at least 60 weight %.
In another aspect, the invention includes a coating including a
resin, optional dispersant, and at least a first carbon black, the
first carbon black having an I.sub.2 number from 25 mg/g to 200
mg/g, a DBP from 20 to 45 cc/100 g, and a concentration of Group IA
and IIA elements, in .mu.g/g, of at most y+(15*I.sub.2 number),
wherein y is 250, 100, -50, -150, or -350. For example, the first
carbon black may have a DBP value of from 20 to 45 cc/100 g, from
20 to 30 cc/100 g, from 25 to 43 cc/100 g, from 25 to 40 cc/100 g,
from 30 to 39 cc/100 g, or a DBP in any range bounded by any of
these endpoints. Alternatively or in addition, the first carbon
black may have an iodine number (I.sub.2 number) of from 30 to 200
mg/g, for example, from 30 to 45 mg/g, from 45 to 100 mg/g, from 60
to 80 mg/g, from 70 to 100 mg/g, from 100 to 150 mg/g, from 150 to
200 mg/g, 70 to 200 mg/g, or in any range bounded by any of these
endpoints. When the coating includes 60 weight percent of carbon
black, it may have a surface electrical resistivity of at least
10.sup.12 ohm/square. The first carbon black may be characterized
by at least one of the following: an M-ratio of from 1 to less than
1.25; a pH from 6 to 10; a water spreading pressure of at most 6
mJ/m.sup.2; or a tint of at least 80. The first carbon black may
have a tint obeying the equation tint=x+0.44*I.sub.2 number, where
x is from 45 to 90, for example, from 60 to 90 or 75 to 90. The
coating may have an optical density of at least 3, for example, at
least 4, at a 1 micron thickness. The coating may include at least
50% by weight of carbon black, for example, at least 55% by weight
of carbon black, from 50% to 80% by weight of carbon black, from
55% to 80% by weight of carbon black, or 60% to 80% by weight of
carbon black.
In another aspect, the invention includes millbase including at
least 20 weight percent carbon black including a first carbon
black, a vehicle, and an optional dispersant. The first carbon
black has an I.sub.2 number from 30 mg/g to 200 mg/g, a DBP from 20
to 45 cc/100 g, and a concentration of Group IA and IIA elements,
in .mu.g/g, of at most y+(15*I.sub.2 number), wherein y is 250,
100, -50, -150, or -350. For example, the first carbon black may
have a DBP value of from 20 to 45 cc/100 g, from 20 to 30 cc/100 g,
from 25 to 43 cc/100 g, from 25 to 40 cc/100 g, from 30 to 39
cc/100 g, or a DBP in any range bounded by any of these endpoints.
Alternatively or in addition, the first carbon black may have an
iodine number (I.sub.2 number) of from 30 to 200 mg/g, for example,
from 30 to 45 mg/g, from 45 to 100 mg/g, from 60 to 80 mg/g, from
70 to 100 mg/g, from 100 to 150 mg/g, from 150 to 200 mg/g, 70 to
200 mg/g, or in any range bounded by any of these endpoints. The
first carbon black may characterized by at least one of the
following: an M-ratio of from 1 to less than 1.25; a pH from 6 to
10; a water spreading pressure of at most 6 mJ/m.sup.2; or a tint
of at least 80. The carbon black may have a tint obeying the
equation tint=x+0.44*I.sub.2 number, where x is from 45 to 90, for
example, from 60 to 90 or 75 to 90. When the millbase is formulated
with 50% by weight carbon black, the millbase may be a Newtonian
fluid. The millbase may include at least 30 weight %, at least 40
weight %, at least 45 weight %, at least 55 weight %, or at least
60 weight %, for example, from 50 weight % to 80 weight % or from
60 weight % to 80 weight % of carbon black, or any amount of carbon
black in any range bounded by any of these endpoints.
It is to be understood that both the foregoing general description
and the following detailed description are exemplary and
explanatory only and are intended to provide further explanation of
the present invention, as claimed.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a graph showing the percolation curves for a carbon black
for use according to an exemplary embodiment of the invention and a
commercially available carbon black.
FIG. 2 is a cross-sectional view of a portion of one type of
furnace carbon black reactor that may be utilized to produce carbon
blacks for use in exemplary embodiments of the invention.
FIG. 3 is a sample histogram of the weight fraction of the
aggregates of a carbon black sample versus the Stokes Diameter in a
given sample.
FIG. 4 is a graph showing the viscosity of millbases produced using
a carbon black according to an exemplary embodiment of the
invention and a commercially available carbon black.
DETAILED DESCRIPTION OF THE INVENTION
We have surprisingly found that coatings including a resin and at
least one carbon black having a low level of structure, e.g., a DBP
of 20 cc/100 g to 45 cc/100 g, can be produced with higher loadings
of carbon black while exhibiting improved electrical properties
compared to coatings comprising the same resin and more highly
structured carbon blacks. Furthermore, we have unexpectedly found
that low structure, high surface area blacks allow the production
of coatings and black matrices with high carbon black loadings
while maintaining control of resistivity.
In one embodiment, a black matrix according to the invention
includes at least a first carbon black, the first carbon black
having a dibutylphthalate absorption (DBP) value, a measure of the
structure or branching of a pigment, from 20 cc/100 g to 45 cc/100
g and an iodine number from 30 mg/g to 200 mg/g.
In certain embodiments, the first carbon black employed in the
black matrix composition and in other embodiments of the invention
described elsewhere herein may have a DBP value of from 20 to 45
cc/100 g, from 20 to 30 cc/100 g, from 25 to 43 cc/100 g, from 25
to 40 cc/100 g, from 30 to 39 cc/100 g, or a DBP in any range
bounded by any of these endpoints. The carbon black primary
particles may approach an essentially overall spherical geometry,
although carbon particles having other shapes, such as needles and
plates, may also be used.
The first carbon black employed in the black matrix composition and
in other embodiments of the invention described elsewhere herein
may have any of a wide range of surface areas depending on the
desired properties of the carbon black. For example, the carbon
black may have an iodine number (I.sub.2 number) of from 30 to 200
mg/g, for example, from 30 to 45 mg/g, from 45 to 100 mg/g, from 60
to 80 mg/g, from 70 to 100 mg/g, from 100 to 150 mg/g, from 150 to
200 mg/g, 70 to 200 mg/g, or in any range bounded by any of these
endpoints. As known to those skilled in the art, at fixed porosity,
increased surface area correlates with smaller primary particle
size.
The first carbon black employed in any of the embodiments of this
invention may additionally have one or more of the following
properties, each of which is discussed in more detail below. The
carbon black may have a total concentration of alkali and alkaline
earth elements (e.g., Group IA and IIA elements) in .mu.g/g, of at
most (y+15*I.sub.2 number), where y is 250, 100, -50, -150, or
-350. The M-ratio, the ratio of the median Stokes diameter to the
mode of the Stokes diameter of a carbon black sample, may be from
1.0 to less than 1.25, for example, between 1.22 and 1.24 or in any
range defined by any of these endpoints. The carbon black may have
a tint of at least 80. The tint of the carbon black may be defined
by the following equation: Tint=x+0.44*I.sub.2 number where x may
be from 45 to 90, for example, from 60 to 90 or from 75 to 90. The
carbon black may have a pH from 6 to 10, for example, from 6 to 8,
from 8 to 10, from 7 to 9, or in any range defined by any of these
endpoints. The water spreading pressure (WSP), a measure of the
interaction energy between the carbon black surface and water
vapor, may be at most 6 mJ/m.sup.2, for example, at most 5
mJ/m.sup.2, at most 4 mJ/m.sup.2, from 2 to 6 mJ/m.sup.2, from 2 to
5 mJ/m.sup.2 from 3 to 6 mJ/m.sup.2, from 3 to 5 mJ/m.sup.2, or in
any range defined by any of these endpoints.
In general, the loading level of a specific carbon black affects
the surface resistivity of a coating containing that carbon black.
Initially, at low loadings, the surface resistivity remains
substantially constant with increasing amounts of carbon black. At
higher levels, a transition occurs in which enough carbon black is
present that a substantial decrease in resistivity occurs. This is
often referred to as the percolation threshold. Levels of carbon
black in excess of this threshold have very little effect on the
resistivity of the coating. Many carbon blacks exhibit similar
percolation performance. Thus, carbon black percolation curves are
very similar, regardless of the type of carbon black, with the
exception that the percolation point (i.e., the loading of carbon
black at which the surface resistivity decreases) is different.
This is shown by a shifting of the percolation curve. FIG. 1 shows
percolation curves for two different coatings produced with the
same resin but different carbon blacks. The percolation curves have
a shape that is common for carbon black, with two relative plateaus
connected by a relatively steep transition region.
For some applications, the target surface resistivity may fall on
the steepest point of the percolation curve. From a practical
perspective, manufacturing this coating would require tight
controls on the carbon black loading since small changes in loading
would have a large effect on the observed resistivity.
Without being bound by any particular theory, it is believed that
the low structure of the carbon blacks exploited in various
embodiments of the invention may enable higher packing efficiency
of the carbon black. Lower structure carbon blacks are
geometrically able to pack more densely than higher structure
carbon black particles, as measured by their DBP oil absorption,
which is an effective measure of their packed pore volume. As a
result, in certain embodiments of the present invention, the
percolation curve may be shifted such that a preselected
resistivity may occur away from the steepest part of the curve.
Thus, small changes in loading do not have a large effect on
resistivity.
The ability to increase carbon black loading provides other
benefits to materials such as toners, inks, black matrix,
photoresist, and millbases used to prepare these and other
products. The performance of the millbase and photoresist depend on
the content of carbon black. As the carbon black concentration is
increased, properties such as curability, developability,
patternability, and adhesion to glass are affected. In many cases,
one of these properties limits the upper concentration of carbon
black that is acceptable in the coating, which in turn imposes an
upper limit on the achievable optical density of the film.
Exploiting low structure carbon blacks according to certain
embodiments of the invention allows the preparation of films with
higher loading of carbon black while maintaining the balance of
properties required for performance as a black matrix. Since the
optical density of the film is proportional to its carbon black
content, we expect that these films formulated at maximum carbon
loading will have comparatively higher optical density than films
prepared with conventional carbon black.
Moreover, we have unexpectedly found that dispersions prepared with
increased concentrations of low structure, high surface area carbon
blacks have relatively lower viscosity than dispersions prepared
with either higher structure or lower surface area blacks. This
improves the manufacturability of various devices. Indeed, we have
found that these dispersions retain Newtonian flow characteristics
at higher loadings than dispersions with higher structure or lower
surface area blacks. The reduced viscosity improves the leveling of
coating compositions, reducing irregularities in the final coating
and increasing smoothness. In addition, thinner coatings may be
deposited without the risk of pinholes or other defects.
We have unexpectedly discovered that use of carbon black having an
M-ratio less than 1.25 increases the optical density of materials
into which the carbon black is incorporated with respect to carbon
blacks having the same structure and surface area but higher
M-ratios. This allows lesser quantities of carbon black to be used
to obtain a given optical density, reducing the viscosity of
millbases and other fluid media containing the carbon black that
are used to produce such materials. Increased tint decreases the
amount of carbon black that must be used in a carrier to achieve a
desired optical density.
Carbon blacks having a neutral pH or slightly basic pH rather than
an acidic pH may be more compatible with certain polymers and other
materials that can be used to produce black matrix, coatings,
millbases, inks, toners, and other media, expanding the range of
compositions that may be combined with carbon black for these
applications. In addition, such carbon blacks will interact
differently with the alkaline developers typically employed in the
production of black matrix than acidic carbon blacks and may
improve the development characteristics of resists, black matrices,
and other coatings employing alkaline developers.
Carbon blacks having a lower quantity of alkali and alkaline earth
elements may exhibit lower conductivity and/or provide higher
optical density to media into which they are incorporated.
Lower WSP represents more hydrophobic carbon black. Carbon blacks
with low water spreading pressures, e.g., more hydrophobic carbon
blacks, may be more compatible with certain polymers and other
materials that can be used to produce black matrix, millbases,
coatings, inks, toners, and other materials, expanding the range of
compositions that may be combined with carbon black for these
applications. In addition, such carbon blacks will interact
differently with the alkaline developers typically employed in the
production of black matrix and resist coatings than more
hydrophilic carbon blacks and may improve the development
characteristics of resists, black matrices, and other coatings
employing alkaline developers.
It has surprisingly been found that millbases, dispersions, curable
coating compositions, and coatings such as black matrix may be
prepared with relatively high levels, e.g., at least 40%, at least
50%, at least 55%, or at least 60% of carbon blacks such as those
described herein. This enables the preparation of coatings and
black matrices having improved overall properties, including an
improved balance of electrical properties such as surface
resistivity, and optical density. Surface resistivity is a measure
of the ability of a material to prevent the conduction of
electricity and can be measured using a variety of techniques known
in the art. Optical density is typically measured using an optical
densitometer. OD is dependent on several factors, including the
thickness of the film.
Carbon blacks such as those described herein may be combined with a
vehicle and a curable resin to form a curable coating composition.
The curable coating composition may be formed using any method
known to those skilled in the art, including, for example, using
high shear mixing. Furthermore, the compositions may be prepared
using a dispersion of carbon black in a vehicle, such as a
millbase. Such a millbase may have at least 20 weight percent, for
example, at least 30 weight percent, of carbon black including a
carbon black such as those described herein. When the millbase
includes 50 weight percent carbon black, it may be a Newtonian
fluid. Preferably, there is sufficient resin in the cured coating
to substantially fill the void volume defined by the shape of the
carbon black aggregates.
The vehicle may be either an aqueous vehicle or a non-aqueous
vehicle. Examples include non-aqueous vehicles including one or
more of butanol (e.g., one or more of n-butanol, sec-butanol,
tert-butanol, and isobutanol), 2-heptanone, butyl acetate,
ethylcellosolve, ethylcellosolve acetate, butylcellosolve,
butylcellosolve acetate, ethylcarbitol, ethylcarbitol acetate,
diethyleneglycol, cyclohexanone, propyleneglycol monomethylether,
propyleneglycol monomethylether acetate, lactate esters, dimethyl
formamide, methyl ethyl ketone, dimethylacetamide, and mixtures
thereof. Aqueous solvents may also be added, including, for
example, water and water soluble alcohols.
The curable resin may be any resin known in the art. For example,
the resin may be an epoxy bisphenol-A resin or an epoxy novolac
resin. The resin may also be an acrylic resin, a polyimide resin, a
urethane resin, a polyester resin, or a gelatin. The resin may be
cured by any of a variety of known methods, including, for example,
thermally or by any source of radiation such as, for example,
infrared or ultraviolet radiation. The curable coating composition
may be photosensitive (i.e. may be cured by irradiation) or
thermosensitive (i.e., may be cured by changing temperature, such
as by heating). When the resin is curable by irradiation, the
curable coating composition may further include a photoinitiator,
which generates a radical on absorbing light with the respective
pigment.
The curable coating composition or millbase may be formed with a
minimum of additional components (additives and/or cosolvents) and
processing steps. However, additives such as dispersants and
cosolvents may also be included. For example, when a photosensitive
resin is used, such as epoxy bisphenol-A or epoxy novolak, a
photoinitiator can also be added. Other curable monomers and/or
oligomers may also be added.
In a further embodiment, a curable coating is prepared from the
curable coating composition. The curable coating may include a
curable resin and at least one carbon black. The curable resin and
the carbon black can be any of those described in more detail
above. The curable coating can be a photosensitive coating from
which a cured coating may be fabricated by irradiating the curable
coating, or a thermosensitive coating, from which a cured coating
is fabricated by thermal treatment of the curable coating.
In another embodiment, a cured coating is prepared from the curable
coating composition. The cured coating may include a resin, an
optional dispersant, and at least one carbon black such as any of
those described herein. When the coating includes at least 60
weight percent of carbon black, the surface electrical resistivity
may be at least 10.sup.12 ohm/square, for example, 10.sup.13
ohm/square. The coating, for example, a black matrix, may further
may have an optical density of greater than or equal to 3,
preferably greater than or equal to 4, and more preferably greater
than or equal to 5, for example, between 3.5 and 10, at a 1 micron
thickness. The coatings may have similar electrical properties
(such as resistivity) at greater film thicknesses, including, for
example, 10-100 micron thickness, depending on the application of
the coating.
The present invention further relates to a black matrix that may be
used in, for example, a color filter in a liquid crystal display
device. The black matrix can be formed using any method known in
the art. For example, the black matrix may be formed by applying a
curable coating composition comprising a first carbon black onto a
substrate, curing the resulting curable coating imagewise to
produce a cured coating, and developing and drying the cured
coating. For example, the black matrix may be prepared from the
curable coating composition, curable coating, and/or the cured
coating of the present invention, each of which is described in
more detail above.
Surface resistivity and optical density are important properties
for black matrix materials, and are described in more detail above.
Since the black matrices according to certain embodiments of the
present invention may be formed from the curable coating
compositions of the present invention, which are used to form a
cured coating of the present invention, the black matrix can have
the performance properties (surface resistivity and optical
density) described above in relationship to the coating. In
addition, carbon black may be selected with a specific DBP to
attain particular desired overall performance attributes.
Performance of the various media described above will depend on a
variety of factors. For example, it has surprisingly been found
that coatings comprising a resin and a first carbon black may be
produced with higher carbon black loadings while maintaining high
resistivity, even when the first carbon black has not been
subjected to additional surface modification. In certain
embodiments, it may be desirable to optimize optical density,
carbon black loading, surface resistivity, smoothness, and other
performance requirements.
Coatings and black matrices according to various embodiments of the
invention may also be produced using blends of carbon blacks. For
example, carbon black blends may include a first carbon black and a
second carbon black with different primary particle sizes. The
difference between the two particle sizes may be from 1 nm to 25
nm, for example, from 5 nm to 25 nm. The smaller particles may fit
in the interstices between larger carbon black particles. One of
skill in the art will recognize that, for a given sample of carbon
black, the particle size will actually exhibit a distribution of
sizes about the specified size. In another embodiment, carbon
blacks having different surface compositions, surface areas, levels
of structure, concentrations of metal elements, pH values, or
Spectronic 20 values may be blended. For example, carbon blacks
that have not been modified to attach an organic group to the
surface or have been oxidized or subjected to heat treatment, e.g.,
to increase the graphite content of the carbon black, may be
combined with carbon blacks that have been subjected to such
modification.
We have identified operating conditions that permit low structure
carbon blacks to be produced with high surface areas but with lower
amounts of Group IA and Group IIA metal elements than have been
previously used, thereby reducing the amount of these metals in the
carbon black product. In general, for a carbon black having a given
surface area, the structure can only be depressed to a certain
amount by addition of metal elements, after which further metal
element addition does not further influence structure. However, we
have produced carbon blacks having significantly lower structure,
e.g., a dibutylphthalate absorption (DBP) value of 20 cc/100 g to
45 cc/100 g, than has been previously achievable for intermediate
surface area blacks, not to mention high surface area blacks.
Exemplary apparatus and reaction conditions are described below and
in the Examples. Carbon blacks for use according to various
embodiments of the invention may also be produced using a variety
of other apparatus, including those described in, for example, U.S.
Pat. Nos. 5,456,750, 4,391,789; 4,636,375; 6,096,284; and
5,262,146. One of skill in the art will recognize how to adapt the
reaction conditions described below to produce carbon blacks for
use according to the various embodiments of the invention in other
apparatus.
In one embodiment, carbon blacks are produced in a modular furnace
carbon black reactor 2, such as that depicted in FIG. 2, having a
combustion zone 10, which has a zone of converging diameter 11,
transition zone 12, entry section 18, and reaction zone 19. The
diameter of the combustion zone 10, up to the point where the zone
of converging diameter 11 begins, is shown as D-1; the diameter of
zone 12, as D-2; the diameters of the stepped entry section, 18, as
D-4, D-5, D-6, and D-7; and the diameter of zone 19, as D-3. The
length of the combustion zone 10, up to the point where the zone of
converging diameter 11 begins, is shown as L-1; the length of the
zone of converging diameter is shown as L-2; the length of the
transition zone is shown as L-3; and the lengths of the steps in
the reactor entry section, 18, as L-4, L-5, L-6 and L-7.
To produce carbon blacks, hot combustion gases are generated in
combustion zone 10 by contacting a liquid or gaseous fuel with a
suitable oxidant stream such as air, oxygen, mixtures of air and
oxygen or the like. Among the fuels suitable for use in contacting
the oxidant stream in combustion zone 10 to generate the hot
combustion gases are any of the readily combustible gas, vapor, or
liquid streams such as natural gas, hydrogen, carbon monoxide,
methane, acetylene, alcohol, or kerosene. It is generally
preferred, however, to utilize fuels having a high content of
carbon-containing components and in particular, hydrocarbons. The
volumetric ratio of air to natural gas utilized to produce the
carbon blacks of the present invention may preferably be from about
10:1 to about 100:1. To facilitate the generation of hot combustion
gases, the oxidant stream may be preheated. In some embodiments,
the overall combustion ratio is at least 26%, for example, at least
30% or at least 35%.
The hot combustion gas stream flows downstream from zones 10 and 11
into zones 12, 18, and 19. The direction of the flow of hot
combustion gases is shown in the figure by the arrow. Carbon
black-yielding feedstock 30 is introduced at point 32 (located in
zone 12), and/or at point 70 (located in zone 11). Suitable for use
herein as carbon black-yielding hydrocarbon feedstocks, which are
readily volatilizable under the conditions of the reaction, are
unsaturated hydrocarbons such as acetylene; olefins such as
ethylene, propylene, butylene; aromatics such as benzene, toluene
and xylene; certain saturated hydrocarbons; and other hydrocarbons
such as kerosenes, naphthalenes, terpenes, ethylene tars, aromatic
cycle stocks and the like.
The distance from the end of the zone of converging diameter 11 to
point 32 is shown as F-1. Generally, carbon black-yielding
feedstock 30 is injected in the form of a plurality of streams
which penetrate into the interior regions of the hot combustion gas
stream to insure a high rate of mixing and shearing of the carbon
black-yielding feedstock by the hot combustion gases so as to
rapidly and completely decompose and convert the feedstock to
carbon black.
Auxiliary hydrocarbon is introduced at point 70 through probe 72 or
through auxiliary hydrocarbon passages 75 in the walls which form
the boundaries of zone 12 of the carbon black forming process or
through auxiliary hydrocarbon passages 76 in the walls which form
the boundaries of zones 18 and/or 19 of the carbon black forming
process. The term "auxiliary hydrocarbon" as used herein refers to
hydrogen or any hydrocarbon having a molar hydrogen-to-carbon ratio
greater than the molar hydrogen-to-carbon ratio of the feedstock
and may be gaseous or liquid. Exemplary hydrocarbons include but
are not limited to those materials described herein as suitable for
use as fuels and/or feedstocks. In certain embodiments of the
invention, the auxiliary hydrocarbon is natural gas. The auxiliary
hydrocarbon may be introduced at any location between the point
immediately after the initial combustion reaction of the
first-stage fuel and the point immediately before the end of
formation of carbon black provided that unreacted auxiliary
hydrocarbon eventually enters the reaction zone. In certain
preferred embodiments, the auxiliary hydrocarbon is introduced in
the same axial plane as the feedstock. In the Examples described
below, the auxiliary hydrocarbon was introduced through three
orifices in the same axial plane as the carbon black yielding
feedstock streams. The orifices are preferably arranged in an
alternating pattern, one feedstock, the next auxiliary hydrocarbon,
etc., spaced evenly around the outer periphery of section 12. The
quantity of auxiliary hydrocarbon added to the reactor may be
adjusted so that carbon content of the auxiliary hydrocarbon is
less than about 20% by weight of the total carbon content of all
fuel streams injected into the reactor, for example, from about 1
to about 5%, from about 5% to about 10%, from about 10% to about
15%, from about 15% to about 20%, or in any range defined by any of
these endpoints. In certain preferred embodiments, the carbon
content of the auxiliary hydrocarbon is from about 3% to about 6%
by weight of the total carbon content of all fuel streams injected
into the reactor.
The distance from point 32 to point 70 is shown as H-1.
In some embodiments, specific alkali or alkaline earth materials
are added to the carbon black as a structure modifier in such an
amount that the total concentration in the resulting carbon black
of alkali or alkaline earth materials is low. Preferably, the
substance contains at least one alkali metal or alkaline earth
metal. Examples include lithium, sodium, potassium, rubidium,
cesium, francium, calcium, barium, strontium, or radium, or any
combination of two or more of these. The substance can be a solid,
solution, dispersion, gas, or any combination thereof. More than
one substance having the same or different Group IA or Group IIA
element can be used. If multiple substances are used, the
substances can be added together, separately, sequentially, or in
different reaction locations. For purposes of the present
invention, the substance can be the metal (or metal ion) itself, a
compound containing one or more of these elements, including a salt
containing one or more of these elements, and the like. Exemplary
salts include both organic and inorganic salts, for example, salts,
e.g., of sodium and/or potassium, with any of chloride, acetate, or
formate, or combinations of two or more such salts. Preferably, the
substance is capable of introducing a metal or metal ion into the
reaction that is ongoing to form the carbon black product. For
instance, the substance can be added at any point prior to the
complete quenching, including prior to the introduction of the
carbon black yielding feedstock in the first stage; during the
introduction of the carbon black yielding feedstock in the first
stage; after the introduction of the carbon black yielding
feedstock in the first stage; prior to, during, or immediately
after the introduction of the auxiliary hydrocarbon; or any step
prior to complete quenching. More than one point of introduction of
the substance can be used. The amount of the metal-containing
substance can be any amount as long as a carbon black product can
be formed. As described above, the amount of the substance can be
added in an amount such that the total amount of Group IA and/or
Group IIA elements (i.e., the total concentration of Group IA and
Group IIA elements contained the carbon black) in .mu.g/g is at
most y+15*I.sub.2 number where y may be 250, 100, -50, -200, or
-350. In certain embodiments, the substance introduces a Group IA
element; for example, the substance may introduce potassium or
potassium ion. The substance can be added in any fashion including
any conventional means. In other words, the substance can be added
in the same manner that a carbon black yielding feedstock is
introduced. The substance can be added as a gas, liquid, or solid,
or any combination thereof. The substance can be added at one point
or several points and can be added as a single stream or a
plurality of streams. The substance can be mixed in with the
feedstock, fuel, and/or oxidant prior to and/or during their
introduction.
In certain embodiments, the substance containing at least one Group
IA or Group IIA element is introduced into the feedstock by
incorporation of a salt solution into the feedstock. In certain
preferred embodiments, salt solutions are mixed with the feedstock
such that the concentration of all alkali metal and/or alkaline
metal ions in the feedstock is from about 0 to about 1 weight
percent. Upon combustion, the metal ions can become incorporated
into the carbon black. Without being bound by any particular
theory, it is believed that the charge of metal ions provides a
repulsive force between individual carbon black particles. This
repulsive force may keep particles from aggregating, thus
decreasing the overall structure of the carbon black.
The mixture of carbon black-yielding feedstock and hot combustion
gases flows downstream through zone 12 into zone 18 and then into
zone 19. Quench 60, located at point 62, injecting quenching fluid
50, which may be water, is utilized to stop the chemical reaction
when carbon blacks are formed. Point 62 may be determined in any
manner known to the art for selecting the position of a quench to
stop pyrolysis. One method for determining the position of the
quench to stop pyrolysis is by determining the point at which an
acceptable Spectronic 20 value for the carbon black is reached. Q
is the distance from the beginning of zone 18 to quench point 62,
and will vary according to the position of quench 60. In some
embodiments, reverse osmosis water is used as the quenching fluid
to minimize the amount of additional metal and other elements that
are added to the carbon black during quenching.
After the mixture of hot combustion gases and carbon black-yielding
feedstock is quenched, the cooled gases pass downstream into any
conventional cooling and separating means whereby the carbon blacks
are recovered. The separation of the carbon black from the gas
stream is readily accomplished by conventional means such as a
precipitator, cyclone separator or bag filter. This separation may
be followed by pelletizing using, for example, a wet
pelletizer.
In the furnace, the specific iodine number and DBP of the carbon
black are controlled by simultaneously adjusting the burner natural
gas rate, feedstock rate, potassium concentration, and auxiliary
hydrocarbon rate and location to achieve the desired properties.
The iodine number can be increased by increasing the burner natural
gas rate, decreasing the feedstock rate, increasing the metal salt
concentration, and/or decreasing the auxiliary hydrocarbon rate.
The DBP can be increased by increasing the burner natural gas rate,
increasing or decreasing the feedstock rate (depending on other
factors), decreasing the metal salt concentration, and/or
decreasing the auxiliary hydrocarbon rate. Where the auxiliary
hydrocarbon is increased e.g., such that it provides more that 8%
or 10% of the total carbon content in the reactor, it may be
desirable to reduce the amount of feedstock in the reactor to
maintain or increase the surface area of the resulting carbon
black. Under these conditions, low structure might also be achieved
with lower amounts of alkali or alkaline earth materials. The
variables discussed herein also affect other characteristics of the
carbon black such as tint, Spectronic 20 value, pH, M-ratio, and
residual metal content. The exact levels of each variable required
to create carbon black with the desired properties depend on the
geometry of the reactor and the method of injection of each species
into the reactor. Examples are described in more detail below.
We have unexpectedly found that certain conditions for introducing
the auxiliary gas, including a decreased injection orifice
diameter, increased feed rate, and injection of the auxiliary gas
in the same axial plane as the carbon-black yielding feedstock, in
combination with specific concentrations of alkali and/or alkaline
earth elements in the feedstock, as well as specific diameters and
lengths for the various combustion zones, enabled us to produce
carbon blacks having both low structure and high surface area. The
blacks are also more hydrophobic than would have been expected from
the reaction conditions employed. The levels of structure are
significantly lower than what can be achieved through the use of
alkali or alkaline earth addition or auxiliary hydrocarbon alone.
Furthermore, the carbon blacks have structures that are
significantly lower, e.g., 20 cc/100 g to 45 cc/100 g, than what
has been previously achievable for intermediate or high surface
area blacks, e.g., 30-200 m.sup.2/g. The amount of alkali or
alkaline earth metals in the carbon black is lower than what is
usually found for lower structure carbon blacks with intermediate
to high surface area. The resulting carbon black has the low DBP
that facilitates dispersion and reduces viscosity of media in which
the carbon black is incorporated to ease manufacturing without a
reduction in surface area, which can decrease optical density in
devices produced from the carbon black. Furthermore, the low level
of alkali and alkaline earth materials further allows low DBP
blacks to be employed in electronic applications without
sacrificing resistivity. The increased tint exhibited by these
carbon blacks decreases the amount of carbon black that must be
used in a carrier to achieve a desired optical density.
In some embodiments, the carbon black may be modified to attach an
organic group to the surface, oxidized, or subjected to heat
treatment. Carbon black may be heat treated in an inert atmosphere
to increase the graphite content of the carbon black. One of skill
in the art will recognize that the time and temperature of the heat
treatment may be adjusted to achieve a desired amount of
graphitization.
Oxidized carbon blacks are oxidized using an oxidizing agent in
order to introduce polar, ionic, and/or ionizable groups onto the
surface. Carbon blacks prepared in this way have been found to have
a higher degree of oxygen-containing groups on the surface.
Oxidizing agents include, but are not limited to, oxygen gas,
ozone, NO.sub.2 (including mixtures of NO.sub.2 and air), peroxides
such as hydrogen peroxide, persulfates, including sodium,
potassium, or ammonium persulfate, hypohalites such a sodium
hypochlorite, halites, halates, or perhalates (such as sodium
chlorite, sodium chlorate, or sodium perchlorate), oxidizing acids
such a nitric acid, and transition metal containing oxidants, such
as permanganate salts, osmium tetroxide, chromium oxides, or ceric
ammonium nitrate. Mixtures of oxidants may also be used,
particularly mixtures of gaseous oxidants such as oxygen and ozone.
In addition, carbon blacks prepared using other surface
modification methods to introduce ionic or ionizable groups onto a
pigment surface, such as chlorination and sulfonylation, may also
be used.
Modified carbon blacks may be prepared using any method known to
those skilled in the art such that organic chemical groups are
attached to the carbon black. For example, the modified carbon
black can be prepared using the methods described in U.S. Pat. Nos.
5,554,739, 5,707,432, 5,837,045, 5,851,280, 5,885,335, 5,895,522,
5,900,029, 5,922,118, and 6,042,643, and PCT Publication WO
99/23174, the descriptions of which are fully incorporated herein
by reference. Such methods provide for a more stable attachment of
the groups onto the carbon black compared to dispersant type
methods, which use, for example, polymers and/or surfactants. Other
methods for preparing the modified carbon black include reacting a
carbon black having available functional groups with a reagent
comprising the organic group, such as is described in, for example,
U.S. Pat. No. 6,723,783, which is incorporated in its entirety by
reference herein. Such a functional carbon black may be prepared
using the methods described in the references incorporated above.
In addition modified carbon blacks containing attached functional
groups may also be prepared by the methods described in U.S. Pat.
Nos. 6,831,194 and 6,660,075, U.S. Patent Publication Nos.
2003-0101901 and 2001-0036994, Canadian Patent No. 2,351,162,
European Patent No. 1 394 221, and PCT Publication No. WO 04/63289,
as well as in N. Tsubokawa, Polym. Sci., 17, 417, 1992, each of
which is also incorporated in its entirety by reference herein.
The following testing procedures are used in evaluating the
analytical and physical properties of the carbon blacks. Iodine
adsorption number of the carbon blacks (I.sub.2 No.) was determined
according to ASTM Test Procedure D-1510-08. Tinting strength (Tint)
of the carbon blacks was determined according to ASTM Test
Procedure D3265-07. The DBP (dibutyl phthalate value) of the carbon
blacks was determined according to the procedure set forth in ASTM
D2414-08. Nitrogen surface area and STSA surface area were measured
as per ASTM D6556-07. Ash content was measured as per ASTM
D1506-99. The pH was determined by dispersing a known amount of
carbon black in water and measuring the pH of the aqueous phase
using a pH probe (ASTM D1512-05). Spectronic 20 was measured as per
ASTM D1618-99. Na and K content were measured via inductively
coupled plasma (ICP) analysis.
The median and mode Stokes diameters were determined from a
histogram of the weight fraction of carbon black versus the Stokes
diameter of the carbon black aggregates, as shown in FIG. 3 and
described in U.S. Pat. No. 5,456,750. Briefly, the data used to
generate the histogram are determined by the use of a disk
centrifuge such as the one manufactured by Joyce Loebl Co. Ltd. of
Tyne and Wear, United Kingdom.
The following procedure is a modification of the procedure
described in the instruction manual of the Joyce Loebl disk
centrifuge file reference DCF 4.008 published on Feb. 1, 1985, the
teachings of which are hereby incorporated by reference, and was
used in determining the data. 10 mg (milligrams) of a carbon black
sample are weighed in a weighing vessel, then added to 50 cc of a
solution of 10% absolute ethanol and 90% distilled water which is
made 0.05% NONIDET P-40 surfactant (NONIDET P-40 is a registered
trademark for a surfactant manufactured and sold by Shell Chemical
Co.). The resulting suspension is dispersed by means of ultrasonic
energy for 15 minutes using Sonifier Model No. W 385, manufactured
and sold by Heat Systems Ultrasonics Inc., Farmingdale, N.Y.
Prior to the disk centrifuge run the following data are entered
into the computer which records the data from the disk
centrifuge:
1. The specific gravity of carbon black, taken as 1.86 g/cc;
2. The volume of the solution of the carbon black dispersed in a
solution of water and ethanol, which in this instance is 0.5
cc.;
3. The volume of spin fluid, which in this instance is 10 cc of
water;
4. The viscosity of the spin fluid, which in this instance is taken
as 0.933 centipoise at 23 degrees C.;
5. The density of the spin fluid, which in this instance is 0.9975
g/cc at 23 degrees C.;
6. The disk speed, which in this instance is 8000 rpm;
7. The data sampling interval, which in this instance is 1 second.
The disk centrifuge is operated at 8000 rpm while the stroboscope
is operating. 10 cc of distilled water are injected into the
spinning disk as the spin fluid. The turbidity level is set to 0;
and 1 cc of the solution of 10% absolute ethanol and 90% distilled
water is injected as a buffer liquid. The cut and boost buttons of
the disk centrifuge are then operated to produce a smooth
concentration gradient between the spin fluid and the buffer liquid
and the gradient is monitored visually. When the gradient becomes
smooth such that there is no distinguishable boundary between the
two fluids, 0.5 cc of the dispersed carbon black in aqueous ethanol
solution is injected into the spinning disk and data collection is
started immediately. If streaming occurs the run is aborted. The
disk is spun for 20 minutes following the injection of the
dispersed carbon black in aqueous ethanol solution. Following the
20 minutes of spinning, the disk is stopped, the temperature of the
spin fluid is measured, and the average of the temperature of the
spin fluid measured at the beginning of the run and the temperature
of the spin fluid measured at the end of the run is entered into
the computer which records the data from the disk centrifuge. The
data is analyzed according to the standard Stokes equation and is
presented using the following definitions:
Carbon black aggregate--a discrete, rigid colloidal entity that is
the smallest dispersible unit; it is composed of extensively
coalesced particles;
Stokes diameter--the diameter of a sphere which sediments in a
viscous medium in a centrifugal or gravitational field according to
the Stokes equation. A non-spherical object, such as a carbon black
aggregate, may also be represented in terms of the Stokes diameter
if it is considered as behaving as a smooth, rigid sphere of the
same density, and rate of sedimentation as the object. The
customary units are expressed in nanometer diameters.
Mode (Dmode for reporting purposes)--The Stokes diameter at the
point of the peak (Point A of FIG. 3 herein) of the distribution
curve for Stokes diameter.
Median Stokes diameter--(Dst for reporting purposes) the point on
the distribution curve of Stokes diameter where 50% by weight of
the sample is either larger or smaller. It therefore represents the
median value of the determination.
The water spreading pressure was measured by observing the mass
increase of a sample as it adsorbs water from a controlled
atmosphere. In the test, the relative humidity (RH) of the
atmosphere around the sample is increased from 0% (pure nitrogen)
to .about.100% (water-saturated nitrogen). If the sample and
atmosphere are always in equilibrium, the water spreading pressure
(.pi..sub.e) of the sample is defined as:
.pi..times..intg..times..GAMMA..times..times.d.times..times.
##EQU00001## where R is the gas constant, T is the temperature, A
is the nitrogen surface area of the sample, .GAMMA. is the amount
of adsorbed water on the sample (converted to moles/gm), P is the
partial pressure of water in the atmosphere, and P.sub.o is the
saturation vapor pressure in the atmosphere. In practice, the
equilibrium adsorption of water on the surface is measured at one
or (preferably) several discrete partial pressures and the integral
is estimated by the area under the curve.
The following procedure may be used to measure the water spreading
pressure. Before analysis, 100 mg of the carbon black to be
analyzed is dried in an oven at 125.degree. C. for 30 minutes.
After ensuring that the incubator in a Surface Measurement Systems
DVS1 instrument (supplied by SMS Instruments, Monarch Beach,
Calif.) has been stable at 25.degree. C. for 2 hours, sample cups
are loaded in both the sample and reference chambers. The target RH
is set to 0% for 10 minutes to dry the cups and to establish a
stable mass baseline. After discharging static and taring the
balance, approximately 8 mg of carbon black is added to the cup in
the sample chamber. After sealing the sample chamber, the sample is
allowed to equilibrate at 0% RH. After equilibration, the initial
mass of the sample is recorded. The relative humidity of the
nitrogen atmosphere is then increased sequentially to levels of
approximately 5, 10, 20, 30, 40, 50, 60, 70, 78, 87, and 92% RH,
with the system allowed to equilibrate for 20 minutes at each RH
level. The mass of water adsorbed at each humidity level is
recorded, from which water spreading pressure is calculated via the
above equation.
The present invention will be further clarified by the following
examples which are intended to be only exemplary in nature.
EXAMPLES
Preparation of Carbon Black
Carbon blacks were prepared in a reactor as described above and
shown in FIG. 2, utilizing the reactor conditions and geometry set
forth in Table 2. Natural gas was employed as both the fuel for the
combustion reaction and the auxiliary hydrocarbon. An aqueous
solution of potassium acetate was used as the alkali
metal-containing material, and was mixed with the feedstock prior
to injection into the reactor. The reaction was quenched with water
purified by reverse osmosis. The liquid feedstock had the
properties indicated in Table 1, below.
TABLE-US-00001 TABLE 1 Feedstock Properties Hydrogen/Carbon Ratio
0.91 Hydrogen (wt %) 6.97 Carbon (wt %) 91.64 Sulfur (wt %) 0.81
Nitrogen (wt %) 0.35 Oxygen (wt %) 0.23 Specific Gravity at
60.degree. F. [ASTM D-287] 1.1029
TABLE-US-00002 TABLE 2 Reactor Geometry and Operating Conditions
Example No. A B C D E D-1 (m) 0.18 0.18 0.18 0.18 0.18 D-2 (m) 0.11
0.11 0.11 0.11 0.11 D-3 (m) 0.91 0.91 0.91 0.91 0.91 D-4 (m) 0.91
0.91 0.91 0.91 0.91 D-5 (m) 0.91 0.91 0.91 0.91 0.91 D-6 (m) 0.91
0.91 0.91 0.91 0.91 D-7 (m) 0.91 0.91 0.91 0.91 0.91 L-1 (m) 0.61
0.61 0.61 0.61 0.61 L-2 (m) 0.30 0.30 0.30 0.30 0.30 L-3 (m) 0.23
0.23 0.23 0.23 0.23 L-4 (m) 0 0 0 0 0 L-5 (m) 0 0 0 0 0 L-6 (m) 0 0
0 0 0 L-7 (m) 0 0 0 0 0 Q (m) 5.0 5.0 4.0 4.0 4.0 Combustion Air
(nm.sup.3/h) 1600 1600 1600 1600 1600 Combustion Air Preheat (K)
753 753 753 753 753 Burner Nat. Gas (nm.sup.3/h) 42 42 42 42 42
Feedstock Injection Orifice Diameter 0.198 0.208 0.150 0.170 0.170
(cm) No. Feedstock Injection Orifices 3 3 3 3 3 Feedstock Rate
(10.sup.4 .times. m.sup.3/s) 1.55 1.68 1.11 1.40 1.30 Feedstock
Temp. (K) 448 443 453 448 468 K.sup.+ Concentration in feedstock
(g/m.sup.3) 274 236 734 780 485 Aux. HC Injection Orifice Diameter
0.508 0.508 0.508 0.508 0.508 (cm) No. Aux. HC Injection Orifices*
3 3 3 3 3 Aux. HC Rate (nm.sup.3/h)** 30 32 22 27 50 Primary
Combustion (%)*** 400 400 400 400 400 Overall Combustion (%)****
25.8 23.7 34.6 28.3 28.9 Quench Water Rate (kg/h) 510 510 520 548
580 *The feedstock and auxiliary hydrocarbon orifices were arranged
in the same axial plane in an alternating sequence around the
periphery of the reactor. HC = hydrocarbon **nm.sup.3 refers to
normal cubic meters, where "normal" refers to the gas volume
corrected to 0.degree. C. and 1 atm pressure ***Primary combustion
is defined as the percentage of oxygen added to the reactor
compared to the total amount of oxygen required to
stoichiometrically react with the burner natural gas. ****Overall
combustion is defined as the percentage of oxygen added to the
reactor compared to the total amount of oxygen required to
stoichiometrically react with all the fuel streams added to the
reactor.
Characterization of Carbon Blacks
Various properties of carbon blacks produced in Example 1 were
measured as described elsewhere herein. The pH values shown were
determined by dispersing 3 g of the material in 30 mL of water,
boiling for 15 minutes, cooling to room temperature, and measuring
the pH of the aqueous phase with a pH probe (ASTM D1512-05). As
shown in Table 3, below, the carbon blacks exhibit low structure,
high purity (low extractables and low [K.sup.+]), neutral to mildly
basic pH, and low WSP (e.g, the carbon blacks are hydrophobic).
TABLE-US-00003 TABLE 3 Example No. A B C D E Iodine Number (mg/g)
47 33 123 73 69 DBP (cc/100 g) 35 32 37 35 37 Nitrogen Surface Area
(m.sup.2/g) 42 105 62 63 STSA Surface Area (m.sup.2/g) 41 31 104 61
63 Tint (%) 87 123 103 105 Spectronic 20 (%) 99.5 75 98 98.5 Boiled
pH 6.6 8.8 7.9 9.2 D-Mode (nm) 84 69 72 D-Stokes (nm)* 103 80 86 Na
content (.mu.g/g) 7.3 K content (.mu.g/g) 434.1 1378 1221 927 Ash
content (wt %) 0.19 WSP (mJ/m.sup.2) 3.0 4.5 3.9 4.9 *Median Stokes
diameter
Preparation of Millbases
The carbon blacks of Example A and a commercially available carbon
black having the characteristics listed in Table 4, below, were
used to prepare millbases with the compositions described in Table
5 below.
TABLE-US-00004 TABLE 4 Comparative Carbon Black Analytical
Properties Example No. C1 Iodine Number (mg/g) 71 DBP (cc/100 g) 46
Nitrogen Surface Area (m.sup.2/g) 66 STSA Surface Area (m.sup.2/g)
66 Tint (%) 104 Spectronic 20 (%) 99 Boiled pH 7.6 D-Mode (nm) 77
D-Stokes (nm)* 87 Na content (.mu.g/g) 191 K content (.mu.g/g) 999
Ash content (wt %) 0.38 WSP (mJ/m.sup.2) 8.0 *Median Stokes
diameter
TABLE-US-00005 TABLE 5 Example No. A C1 Amt of pigment (g) 15 15
Amt of Solsperse 7.5 7.5 32500 (g) (40% solution) Amt of PGMEA (g)
52.5 52.5
Solsperse 32500 is a polymeric dispersant commercially available
from Noveon, and PGMEA is propylene glycol methyl ether acetate
available from Sigma-Aldrich.
The components were milled using a Skandex lab shaker for 4 hours.
The mean volume particle size of the pigments in the millbases were
measured and found to be comparable to the aggregate size of base
carbon black.
Preparation of Letdowns
Each of the millbases of described above were letdown with a 20 wt
% solution of Joncryl 611 (commercially available from Johnson
Polymers) in PGMEA to prepare coating compositions containing 50%
carbon black by weight on a solvent-free basis.
Preparation of Coatings
The coating compositions described above were spin coated onto
glass wafers to form coatings, and the properties of these coatings
were measured. Optical density was measured using an X-Rite 361T
Transmission Densitometer, and the thickness was measured using a
KLA Tencor Alpha Step 500 Surface Profilometer. The surface
resistivity of the coatings was measured using a Keithley Model
6517 Electrometer/High Resistance Meter. Performance properties of
each of the coatings are shown in Table 6 below.
TABLE-US-00006 TABLE 6 Surface Resistivity, Example No. OD at 1
.mu.m .OMEGA./square A 3.6 2.2E+13 C1 3.64 5.05E+13
While these examples use a resin that is not curable, it would be
expected that similar performance would result if a curable resin,
such as a photosensitive or thermosensitive resin, were used.
Therefore, these coatings could be used as a black matrix.
Viscosity
The carbon blacks of Example A and Comparative Example C1 were used
to prepare millbases with from 10 to 50 wt % carbon black in PGMEA.
The millbases also included a dispersant (Solsperse 32500). The
ratio between the dispersant and the carbon black was fixed at 0.2.
The components were milled using a Skandex lab shaker for 4 hours.
The mean volume particle size of the pigments in the millbases were
measured and found to be comparable to the aggregate size of base
carbon black.
Viscosity measurements were conducted for millbase formulations
using cuvette geometry and an AR-G2 (TA Instruments) rheometer.
The millbase dispersions were Newtonian fluids. At 50% loading, the
dispersion with Carbon Black C1 exhibited non-Newtonian behavior,
whereas the dispersion with Carbon Black A was Newtonian in the
entire range of carbon black concentrations studied. A key
advantage of low DBP carbon black is significantly lower viscosity,
especially at higher carbon black loadings (see FIG. 4), which is
beneficial for processing (for instance, by spin coating), and film
properties (for example, film smoothness resulting from to better
leveling off of a lower viscosity coating).
Percolation Curve
The carbon black of Example A and Comparative Example C1 were used
to prepare millbases, letdowns, and coatings according to the
procedures described above and containing 40%, 50%, 60%, 70% carbon
black by weight on a solvent-free basis. The surface resistivity of
the coatings was measured as above and is illustrated in FIG. 3.
FIG. 3 shows that, using lower structure blacks, loading levels can
be increased without either lowering resistivity or creating high
sensitivity of the surface resistivity to loading level.
The foregoing description of preferred embodiments of the present
invention has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Modifications and
variations are possible in light of the above teachings, or may be
acquired from practice of the invention. The embodiments were
chosen and described in order to explain the principles of the
invention and its practical application to enable one skilled in
the art to utilize the invention in various embodiments and with
various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention be
defined by the claims appended hereto, and their equivalents.
* * * * *